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Democritus
Discovered that everything is composed of "atoms", which are physically indivisible and helped lead to the development of modern atomic theory. -
Isaac Newton
In Physics he is widely considered to be the most influential physicist of all time. In optics he showed white light can be split into colors and recombined into white light and improved the reflecting telescope. In mechanics he was able to explain the motion of the planets in terms of 3 laws of motion (now known as Newton's Laws) and a universal theory of gravity. -
John Dalton
Dalton proposed the existence of atoms. He only listed 6 elements but he assigned an Atomic Weight of 1.0 to Hydrogen and then proposed weights for Oxygen, Nitrogen, Carbon, Sulfur, and Phosphorus. He further postulated that chemical combination takes place between particles of different weights. Also, in 1803, John Dalton created the law of multiple proportions that states that when two elements can combine to form more. -
George Johnstone Stoney
Stoney estimated the number of molecules in a cubic millimetre of gas, at room temperature and pressure, from data obtained from the kinetic theory of gases. Stoney's most important scientific work was the conception and calculation of the magnitude of the "atom of electricity". In 1891, he proposed the term 'electron' to describe the fundamental unit of electrical charge, and his contributions to research in this area laid the foundations for the eventual discovery of the particle by J.J. Thoms -
Joseph John Thompson
Until 1897, scientists believed atoms were indivisible, the ultimate particles of matter, but Thomson proved them wrong when he discovered that atoms contained particles known as electrons which he found with cathode rays. In 1913, he channelled a stream of ionized neon through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path.Thomson observed two patches of light on the photographic plate, which suggested two different isotopes -
Max Planck
He is considered to be the founder of the quantum theory, and thus one of the most important physicists of the twentieth century.Then Planck showed that in order to establish a law of heat radiation (Infra red light waves) consonant with experience, it was necessary to employ a method of calculation whose incompatibility with the principles of classical physics became clearer and clearer. For with this method of calculation, Planck introduced into physics the quantum hypothesis, which has since -
Hantaro Nagaoka
Nagaoka rejected Thomson's model on the ground that opposite charges are impenetrable. He proposed an alternative model in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings. Nagaoka's model was, in fact, unstable and it was left to Ernest Rutherford and Niels Bohr, a decade later, to present a more viable atomic model. -
Millikan
Millikan discovered the mass and charge of the electron
To do this, he built a spray to spray oil droplets. As the droplets came out of the nozzle they would become electrically charged by friction. He would then choose one of the droplets and measure the speed at which it was falling. He would then switch on an electrostatic field, and adjust it until the droplet stopped falling. -
Ernest Rutherford
Physicists knew that the atom contained positive and negative charges in equal numbers, but not how they were distributed. Rutherford tried firing a narrow stream of alpha particles at a thin gold foil and detecting where they came out. He thought that the particles would go through the foil, but some would be deflected slightly by passing close to an electron in an atom. -
Henry Moseley
Moseley found that atoms of each element contain a unique positive charge in their nucleus. This discovery helped to solve the mystery of what makes the atoms of one element different from those of another: An atom's identity comes from the number of protons in its nucleus. -
Niels Bohr
Niels Bohr put forward his picture of the atom in 1913. He used Max Plank's quantum theory and suggested that electrons can have only certain amounts of energy, and their orbit can have onlt certain radii and that the electrons which absorb photons move to higher orbits. He also assigned quantum numbers too the orbits. -
James Chadwick
In 1932 Chadwick made a fundamental discovery in the domain of nuclear science: he discovered the particle in the nucleus of an atom that became known as the neutron because it has no electric charge.Unlike positively charged alpha particles, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements. -
Lise Meitner, Hahn Strassman
Meitner, Hahn, and another chemist, Fritz Strassmann, who had worked with the partners since 1929, were deeply involved in identifying the products of neutron bombardment of uranium and their decay patterns. It was generally expected that elements close in atomic number—quite possibly elements with higher atomic numbers than uranium—would be produced. -
Glenn Seaborg
For several years, Seaborg conducted important research in artificial radioactivity using the Lawrence cyclotron at UC Berkeley. He was excited to learn from others that nuclear fission was possible—but also chagrined, as his own research might have led him to the same discovery. He followed Frederick Soddy's work investigating isotopes and contributed to the discovery of more than 100 isotopes of elements.
